1. Field of the Invention
The present invention relates generally to the fields of applied physics and chemical vapor deposition of dielectric films. More specifically, the present invention relates to a method of low temperature integration of a tantalum oxide dielectric film by metalorganic chemical vapor deposition to form thin film metal-insulator-metal (MIM) capacitors.
2. Description of the Related Art
The current trend toward higher density memories in DRAM capacitors, together with the concomitant shrinking of device geometry and decrease in feature size to 0.35 xcexcm or less, precludes the use of conventional dielectrics such as silicon dioxide (SiO2) and silicon nitride (Si3N4). The low dielectric constants for silicon oxide and silicon nitride indicate the inability of these materials to provide sufficient storage capacitance. The next generation DRAM technology requires much higher dielectric constant materials with low dielectric loss. In addition, these conditions must be met for very thin films, i.e.,  less than 100 xc3x85 thick, in order to achieve sufficient capacitance density.
State-of-the-art storage capacitors use various high dielectric constant (k) ceramic and ferroelectric films, such as tantalum oxide (Ta2O5), barium strontium titanate (BST), strontium titanate (SrTiO3), and lead zirconium titanate (PZT). Of these, tantalum oxide (kxcx9c25) is emerging as the preferred material for next-generation memory devices. Although barium strontium titanate has a k value of roughly 400, it is more difficult to integrate in devices than tantalum oxide and will likely not be used in production before the year 2005. Of course, tantalum oxide presents its own unique set of materials integration challenges. For example, it can be difficult to control the defect density in as-deposited Ta2O5 films. This results in high leakage currents and necessitates the subsequent annealing of the film to increase oxygen content and reduce carbon levels.
If the films are being deposited as capacitor dielectrics for DRAM applications, conformal coverage of high aspect ratio structures is generally required; therefore it is advantageous to use a chemical vapor deposition (CVD) process, preferably using a metal-organic precursor. Currently, tantalum oxide films are deposited using tantalum pentaethoxide (TAETO) and oxygen in a metal-organic CVD application. When these thin dielectric films are deposited, variations in composition arising mainly from vacancies at the anionic (oxygen) sites result in characteristically high leakage current densities. Annealing the film in an oxidizing environment serves in part to fill these vacancies and decrease the leakage current density. However, the presence of oxygen in both the deposition and annealing steps can also cause formation of interfacial oxides or oxynitrides between the dielectric and underlying electrode.
An effective dielectric film provides both a low leakage current and high capacitance density. Annealing the deposited Ta2O5 film in a strong oxidizing environment improves the J-V characteristics, but can decrease the capacitance density due to the growth of parasitic oxides and/or oxynitrides at the dielectric/electrode interface. Additionally, for the common case of a doped polycrystalline silicon electrode, the annealing process typically used in conjunction with Ta2O5 is a rapid thermal oxidation (RTO) carried out at the relatively high temperature of about 800xc2x0 C. This particular anneal process results in a Ta2O5 film with reduced leakage current, when compared to the as-deposited film, but also with a much lower capacitance density. Furthermore, this type of high temperature rapid thermal oxidation cannot be used with some common metal nitride electrodes (e.g. titanium nitride, tantalum nitride), due to their high sensitivity towards oxidation at temperatures greater than about 450xc2x0 C. Therefore, it is advantageous to integrate a tantalum oxide dielectric film at a low temperature in such a way as to provide both low leakage current and high capacitance densities.
As described in part above, the prior art is deficient in the lack of an effective method for the low-temperature integration of a tantalum oxide dielectric film for MIM capacitors using an oxygen-free liquid precursor in a MOCVD application. The present invention fulfills this long-standing need and desire in the art.
One embodiment of the present invention provides a method of integrating tantalum oxide into an MIM capacitor for a semiconductor device, comprising the step of vapor-depositing the tantalum oxide from an oxygen-free liquid precursor and under process conditions comprising a deposition temperature of less than about 500xc2x0 C. and a deposition pressure of less than about 96 Torr, so that the tantalum oxide is integrated into the MIM capacitor.
Another embodiment of the present invention provides a method of integrating tantalum oxide into a MIM capacitor for a semiconductor device, comprising the steps of vapor-depositing the tantalum oxide from an oxygen-free liquid precursor and under process conditions comprising a deposition temperature from about 300xc2x0 C. to about 500xc2x0 C. and a deposition pressure from about 0.5 Torr to about 96 Torr; and, annealing the tantalum oxide at a temperature less than about 450xc2x0 C., such that the tantalum oxide is integrated into the MIM capacitor.
Yet another embodiment of the present invention provides a method of forming an MIM capacitor comprising the step of integrating a tantalum oxide dielectric film with a tantalum nitride or a titanium nitride bottom electrode deposited on a substrate and a tantalum nitride or titanium nitride top electrode thereby forming an MIM capacitor.
Yet another embodiment of the present invention provides a method of forming an MIM capacitor comprising the step of integrating a tantalum oxide dielectric film with a tantalum nitride or a titanium nitride bottom electrode deposited on a substrate and a tantalum nitride or a titanium nitride top electrode; where the tantalum oxide dielectric film is formed by the steps comprising vapor-depositing the tantalum oxide from an oxygen-free liquid precursor and under process conditions comprising a deposition temperature from about 300xc2x0 C. to about 500xc2x0 C. and a deposition pressure from about 0.5 Torr to about 96 Torr; and, annealing the tantalum oxide at a temperature less than about 450xc2x0 C., wherein the integration of the tantalum oxide dielectric film forms an MIM capacitor.
Other and further aspects, features, and advantages of the present invention will be apparent from the following description of the presently preferred embodiments of the invention given for the purpose of disclosure.